430 ‘AGRICULTURAL REPORT. 
of man, and consequently it was regarded as useless to enrploy mantres drawn from 
other sources. The Hohenheim managers drew from their tands large supplies, but 
took no care to compensate the soil by imported manures. But if soon appeared, and 
in an alarming manner, that their skill, so highly prized, bad lost its power over these 
fields. So long as the soil remained rich, it reciprocated the care bestowed upon it; 
but, when it became poor, appeals were in vain. The directors imagined that it was 
nature that had changed; that climate and season, before so favorable, had become un- 
accountably hostile to their efforts; nevertheless, and as if they thought that farm ma- 
nure produced crops, and that they only wanted this material in order to obtain better 
harvests, they sought to remedy the evil by making a larger quantity of farm-yard 
manure, which they were able todo. During the years 1852 to 1841 they employed at 
Hohenheim only one-fifth of the farm-yard manure, and yet obtained from the same 
, amount of land under cultivation 20 per cent. more corn than in the years 1854-1860. 
It is easy to understand thisdecrease. By the sale of cereal produce, the fields of Ho- 
henheim lost, between 1821 and 1860, 108, 000 pounds of phosphoric acid which had not 
been restored; the absence of one of the elements which are specially essential to the 
production of wheat became very conspicuous in the diminntion of the harvests. To 
keep tle harvests constantly to the same level, it would be necessary to give to the 
fields of Hohenheim 396,000 pounds of bone dust; so the working of the Hohenheim 
lands, being considered a model of excellence and recomraended for imitation, “has 
proved very clearly that when nutritive principles are carried off the farm, and no 
compensation is given to the land, the soil, however good, will, little by little, lose its 
productiveness.* , 
Almost daily in the agricultural journals we read of experiments made 
with chemical manures, and the terms chemical manures and comple- 
mentary manures have become stereotyped phrases, unknown thirty or 
forty years ago. In fact it was not known then how plants grow, or 
what they feed on. It only needs a slight glance back to the opinions of 
the guiding spirits in agricultural progress to ascertain how vague and 
unsatisfactory was the information on mineral substances as food for 
plants. While we are yet in much obscurity in regard to plant food, we 
are still far beyond the first and second quarter of this century in our 
knowledge of the wants of growing plants. Sir Humphry Davy was much 
in advance of his time on notions of agricultural chemistry, yet even he 
had very vague notions on the relation which the mineral matters of 
the soil bore to the growing plant, and his idea of a manure was that it 
should be of an animal or vegetable nature. In his first lecture he says: 
“Plants are found by analysis to consist principally of charcoal and aeriform mat- 
ter,” and that the principles which they yield, on burning or distillation, were derived 
from elements “ which they gain either by-their leaves from the air or by their roots 
from the soil. All manures from organized substances contain the principles of vegeta- 
ble matters, which, during putrefaction, are rendered either soluble in water or aeri- 
form, and in these states they are capable of being assimilated to the vegetable organs. 
No one principle affords the pabulum of vegetable life; it is neither charcoal nor hy- 
drogen, nor azote, nor oxygen alone, but all of them together in various states and 
various combinations.” 
Here, while he enunciates broad principles truly, he narrows the nu- 
trition of the plant to carbon, hydrogen, azote, and oxygen, and their 
combinations as the essential necessities of a manure, and says that veg- 
etable substances decomposing are the true manures, because they yield 
these elements. When he treats of gypsum, alkalies, and saline sub- 
stances, or simple manures, as he calls them, he says their action is very 
obscure, and likens them to condiments or stimulants in the animal 
economy, which render the common food more nutritive, but never states 
that they are the food of plants. He approaches closely to Liebig’s 
idea when he alludes to the operation of the true alkalies, whose mode 
of action he thought was most simple and distinct. He says: “They 
are found in all plants, and may, therefore, be regarded as their essen- 
tial elements.” But he loses this idea and adds, “they may be useful in 
introducing various principles into the sap of vegetables which may be 
* Translation from vol. viii, International Jury Reports of Paris, 1867; p. 221. 
